Method of converting ethanol to base stock for diesel fuel

ABSTRACT

A method of converting ethanol to a diesel fuel base stock comprises:  
     a reaction stage (a) of contacting the ethanol with an acid catalyst, amorphous or structured, predominantly mesoporous, for example at a temperature of 300° C. to 500° C., at a pressure of 2 to 10 MPa and at a WHSV of 0.2 to 4 h −1 , producing a gas phase, an organic liquid phase and an aqueous liquid phase, and a stage (b) of separating said gas phase, said organic liquid phase and said aqueous liquid phase at a pressure close to the reaction pressure. The method can involve recycling at least part of the gas phase separated in stage (b) to stage (a), and hydrogenating at least part of the organic liquid phase separated in stage (b).

FIELD OF THE INVENTION

The present invention relates to the conversion of ethanol to a dieselfuel base stock.

It more particularly relates to a catalytic method of convertingethanol, pure or containing water, to a diesel fuel base stock.

BACKGROUND OF THE INVENTION

There is an increasing demand for the use of biomass for partlyreplacing petroleum resources for the synthesis of fuels. The use ofbioethanol for the synthesis of base stocks for fuels therefore arousesa great interest. The production of liquid hydrocarbons on acid solidshas been mentioned by some authors during ethanol conversion reactions(H. Van Bekkum et al., Applied Catalysis, 3 (1982)). However, they tookno interest in the optimization of the gas oil yield.

The reaction at the root of the method of converting ethanol to a basestock for diesel fuel is dehydration-oligomerization of the ethanol in asingle stage according to Equation (1) below:2C₂H₅OH→2CH₂CH₂+2H₂O→oligomerization/cyclization (aromatics, paraffins,olefins, etc.)   (1)

It is well known that dehydration of ethanol occurs quite easily on acidsolids of low acidity at temperatures above 300° C. and at atmosphericpressure. The reaction products are then mainly water and ethylene,ethylene being obtained with a selectivity above 96%. The most commonlyused catalysts are silica-aluminas, unprocessed zeolites (ZSM-5) orzeolites modified by steaming, or asbestos-derived zeolites. The use ofa triflic acid-treated ZSM-5 zeolite (R. Le Van Mao et al., TheBioethanol-to-Ethylene (B.E.T.E.) Process, Applied Catalysis, 48(1989)), or of a microporous niobium silicate AM-11 (P. Brandao et al.,Dehydration of Alcohols by Microporous Niobium Silicate AM-11, CatalysisLetters, 80, 3-4 (2002)) have also been mentioned in the prior art. Arelatively old study mentions the production of aromatics up to 50% sfrom ethanol over ZSM-5 at temperatures above 260° C. For lowertemperatures, only the formation of ethylene is mentioned. The presenceof water in the ethanol feedstock seems to promote the formation ofaromatics, in opposition to the conclusions of A. T. Aguayo et al. (J.Chem. Technol. And Biotechnol., 77 (2002)). The presence of water wouldalso have the effect of limiting the deactivation of thecatalyst^((5,6)). On the other hand, for temperatures above 450° C.,there is a risk of catalyst dealumination.

Ethylene oligomerization requires high pressures, generally rangingbetween 2 and 4 MPa, but lower temperatures, generally between 20° C.and 200° C. The catalysts used are in most cases transition metalsdeposited on silica-alumina type supports, zeolites (ZSM-5) ormesoporous solids (MCM-41) as described by V. Hulea et al., J. Catal.,225 (2004).

Few authors have reported the dehydration-oligomerization of ethanol ina single stage. The few studies mentioned (S. Sivasanker et al., S.Assam Science Society, 36(3), (1994) or D. R. Whitcraft et al., Ind.Eng. Chem. Process Dev., 22, (1983)) thus show the production ofgasoline cuts by reaction of ethanol at high pressure and temperature 20over ZSM-5. However, the yields obtained are rather low and the heavycut (T_(boiling)>220° C.) represents a small percentage (<3%). Theformation of aromatics is mentioned: it depends on the pressure and onthe Si/Al ratio of the zeolite. Advanced kinetic studies concerning theconversion of aqueous ethanol over H-ZSM-5 zeolites to hydrocarbons werecarried out by A. T. Aguayo et al. as mentioned above. However, thereactions occur at atmospheric pressure and at high temperature; theproducts obtained are not detailed, but their molecular mass is low(C5+).

The reaction of converting ethanol to produce hydrocarbons(dehydration-oligomerization in a single stage) has mainly been studiedon ZSM-5 zeolite (M. M. s Chang et al., “The Conversion of Methanol andOther O-Compounds to Hydrocarbons over Zeolite Catalysts”, J. Catal. 47,249-259). The main goal was to produce gasoline type effluents, but noauthor attempted to optimize the yield in liquid hydrocarbons with aboiling point temperature above 150° C.

K. G. Bhattacharyya et al. (“Production of Hydrocarbons from AqueousEthanol over HZM-5 under High Pressure”, Journal of Assam ScienceSociety 36(3), pp 177-188 (1994)) are the only ones who took an interestin the results in terms of diesel cut production. However, they have nottried to optimize the operating conditions or the catalyst. The testswere carried out at 3 MPa and 400° C. on an H-ZSM-5 zeolite of Si/Alratio 103, i.e. of relatively low acidity. The diesel cut fraction(270-370° C.) obtained is then only 0.6%. The operating conditions varya lot from one study to the next but the pressure generally favours theformation of liquid products (>C5+), temperatures above 350° promote theoligomerization of ethylene, the primary product from the reaction ofethanol from 300° C. Above 350° C., the formation of aromatics becomessignificant, notably over H-ZSM-5. This catalyst is by far the moststable of all the zeolites studied (mordenite, Y or beta).

The addition of metals by ionic exchange has been studied by J. F.Schulz et al. (“Conversion of Ethanol over Metal-exchanged Zeolites”,Chem. Eng. Technol. 16 (1993) 332-337), who showed the influence ofnickel on the formation of aromatics. According to them, addition ofthis metal allows to stabilize the aluminium sites of the zeolites, thuspreventing crystallinity loss. A low Si/Al ratio of the catalyst favoursthe formation of aromatics. According to Valle B. et al. (“Effect ofNickel Incorporation on the Acidity and Stability of HZSM-5 Zeolite inthe MTO Process”, Catalysis Today 106 (2005) 118-122), in the case ofthe “Methanol to Olefins” process, which requires a high temperature andtakes place in the presence of a large amount of water, addition ofnickel by impregnation allows the H-ZSM-5 zeolite to be stabilized. Thepresence of nickel causes the acidity of the catalyst (strength andnumber) to fall. However, a 1% nickel content allows the catalyst to bemade regenerable without activity loss, unlike the parent solid thatdeactivates. Machado et al. (“Obtaining Hydrocrabons from Ethanol overIron-modified ZSM-5 Zeolites”, Fuel 84, 2064-2070) modified a ZSM-5 ofSi/Al ratio 20 (previously exchanged to obtain the protonic form) byimpregnation with Fe(NO₃)₃, 9H₂O) or by ion exchange with FeCl₃, 6H₂O.

The ZSM-5 zeolite is considered to be microporous since the major partof its pores is smaller than 20 Å.

On the other hand, some authors have compared the dehydration andoligomerization mechanisms of ethanol and of methanol. Derouane et al(J. Catal, 53, 40-55 (1978)) notably showed that the behaviour of thesetwo alcohols in the conversion reaction over acid solids was different.Thus, under identical conditions, at 250° C., more than 98% of theethanol is converted to ethylene whereas the main product detected frommethanol (74%) is dimethyl ether. Espinoza et al (App. Catal, 6, 11-26(1983)) show that 93% of the ethanol is converted to ethylene at 380° C.and 49% of the methanol is converted to C5+.

The mechanism is obviously different for the two alcohols: in fact,methanol first has to react with itself to form dimethyl ether byeliminating a first water molecule, then the elimination of a secondwater molecule allows to obtain the ethylene that can thereafter growvia the formation of a longer ether (by addition of a methoxy group on aC₂ carbocation thus leading to the formation of propylene), or byreaction with another ethylene molecule.

Above 300° C., the conversion of ethanol predominantly goes through theformation of ethylene (directly produced by intramolecular dehydrationof the alcohol or via the diethyl ether), the growth of the chains thusoccurring via carbocationic intermediates (formation of even chains).

In conclusion, the state of the art as regards patent applications for amethod allowing conversion of ethanol to a base stock for diesel fuel bymeans of dehydration-oligomerization in a single stage comprises nopertinent anteriority. The scientific literature essentially took aninterest in the conversion of ethanol to an aromatic base, insofar asthe diesel fraction obtained did not exceed 1% by mass.

OBJECT OF THE INVENTION

One objective of the method according to the invention is to convertethanol feestocks, possibly produced biologically, predominantly tohydrocarbon base stocks that can be blended in the diesel pool in asingle reaction stage, without any stability problem or need to addcompatibilizers to obtain homogeneous mixtures.

Another objective of the invention is to keep all the reaction productsat the various reaction stages without bringing any change to theoperating conditions to separate the aqueous phase. The water formedduring the dehydration stage must be able to remain in the form of gasin the reactor(s) used, without condensing in liquid form between thedehydration and the oligomerization stage. Thus, even if severalreactors are used, one advantage of the invention is that it requires nodecantation of the water between the various reactors, and that is thusallows to perform the most complete conversion possible of ethanol tobase stock for gas oil, while keeping the water formed by the reactionin gaseous form.

Surprisingly enough, it has been discovered that, contrary to what couldbe expected from the prior art, the catalysts allowing conversion ofethanol to a base stock for diesel fuel are catalysts of moderateacidity.

SUMMARY OF THE INVENTION

The method of the invention can be defined as a method of convertingethanol to a base stock for diesel fuel, comprising:

-   a reaction stage (a) of contacting the ethanol with an acid    catalyst, amorphous or structured, predominantly mesoporous, i.e.    comprising at least 60% pore whose size ranges between 2-50 nm,    producing a gas phase, an organic liquid phase and an aqueous liquid    phase, and-   a stage (b) of separating the gas phase, the organic liquid phase    and the aqueous liquid phase at a pressure close to the reaction    pressure.

According to the invention, it has been surprisingly possible to finddifferent catalysts, of variable acidity, amorphous or structured,predominantly mesoporous, allowing to convert the ethanol to a basestock for diesel fuel in a single reaction stage.

What is referred to as mesoporosity is a range of pore sizes from 2 to50 nm. This porosity is measured by mercury or nitrogen intrusionvolume. A predominantly mesoporous compound according to the inventioncomprises at least 60% mesopores and preferably at least 70% mesopores.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 diagrammatically shows the dehydration-oligomerization methodaccording to the present invention in the direct version thereof,without recycling.

FIG. 2 diagrammatically shows a variant of the method according to theinvention involving a stage of recycling at least part of the gas phaseseparated after the dehydration-oligomerization reaction.

FIG. 3 diagrammatically shows a variant of the method according to theinvention involving hydrogenation of at least part of the organic liquidphase separated after the dehydration-oligomerization reaction.

FIG. 4 represents a simulated distillation curve of the organic yieldscorresponding to the balances made in the Example 2 according to theinvention.

DETAILED DESCRIPTION

The method according to the invention relates to various ethanolfeedstocks, possibly produced biologically, containing variableproportions of water. For information, Table 1 hereafter givesconventional compositions of the ethanol batches that can be used asfeedstocks for the method according to the invention. TABLE 1 Feedstocktype Top quality EtOH Crude EtOH Analyses Total sulfur mg/l <0.2 <0.2Total nitrogen mg/l <1 5.4 Na mg/l 0.86 0.8 Ca mg/l 0.41 1.09 Mn mg/l<0.02 <0.02 Fe mg/l 0.15 <0.03 Cu mg/l <0.05 0.08 Zn mg/l 0.03 0.03Analyses Alcohol strength % vol 96.3 92.9 (at 20° C.) Total acidity(acetic acid) 0.8 0.4 Dry extract g/hl 2 3.9 Fixed acidity g/hl <0.1<0.1 (H2SO4) Esters g/hl <0.1 12.3 Acetaldehyde/acetal sum 4.25 10.8(acetaldehyde) Methanol g/hl <0.05 9.4 Butanol-2 g/hl <0.05 <1.0Propanol-1 g/hl <0.1 58.1 Methyl-2 Propanol-1 g/hl n.d. 30.4 Propen-2ol-1 g/hl <0.05 <1.0 Butanol-1 g/hl n.d. <1.0 Methyl-2 butanol-1 g/hln.d. 27.3 Methyl-3 butanol-1 g/hl <0.05 58.2 Methyls-butanol-1 g/hl <0.185.5 Total higher alcohols g/hl 174.6 Volatile nitrogenated bases* mg/kg<0.2 1.2 Aspect limpid-colourless limpid-colourless*The results given in mg/kg are expressed in relation to the anhydrousproduct

In dehydration-oligomerization reaction stage (a) of the methodaccording to the invention, the catalyst is generally selected fromamong the delta, gamma and eta aluminas, mesoporous and macroporous,with a majority of mesopores, and the silica-aluminas.

Gamma or delta aluminas can be used more particularly, obtained bygranulation or extrusion and meeting the external surface area criteriaranging between 130 and 350 m²/g and the pore volume criteria, measuredby mercury intrusion, ranging between 0.3 and 1.2 cm³/g. Alumina, forexample gamma alumina, shaped by means of the “Oil Drop” process, ispreferably used. Catalyst IS463 marketed by the Axens company (formerlyProcatalyse) can be mentioned as a good catalyst for this conversion. Itcorresponds to a gamma alumina catalyst having an external surface areaof 200 m²/g and a pore volume of 0.59 cm³/g. A possible process forshaping these balls is described in patents GB-B-2134536, EP-B-01 5801and EP-B-097539.

These solids can thereafter be treated by silica so as to becomeamorphous silica-aluminas, this method being known to the man skilled inthe art for increasing the hydrothermal stability of catalysts. U.S.Pat. No. 5,545,793 describes the method of preparation for such a solid.

Finally, amorphous silica-aluminas with a silica ratio ranging between10 and 90% by mass and having an external surface area of the order of200 to 480 m²g (SBET measurement) have a good resistance to the partialpressure of water generated by the initial dehydration reaction. Thesilica-alumina Siralox 30 marketed by the Condea Company can for examplebe mentioned as a solid that can be used for the application described.The porosity, measured by mercury intrusion, of a solid of this typeranges between 0.5 and 1.5 cm³/g. Also in the case of silica-aluminas,those whose pore size distribution shows the presence of mesopores andof macropores, with a majority of mesopores, will be used.

In stage (a) of the method according to the invention, the catalyst isgenerally contacted with the fresh ethanol under the reactionconditions, generally at a temperature ranging between 300° C. and 500°C., and at an absolute total pressure ranging between 2 and 10 MPa, theWHSV (weight hourly space velocity, i.e. weight of s feedstock perweight of catalyst and per hour) delivery of the ethanol feedstock onthe catalyst ranging generally between 0.2 and 4 h⁻¹.

The method according to the invention is described hereafter in itsfirst variant, in connection with FIG. 1.

Feedstock (1) contains ethanol and water, with a proportion of ethanolof at least 40% by mass. A feedstock containing at least 90% by mass ofethanol is preferred. This feedstock is brought to the reactionconditions by a set of pumps, heat exchangers and ovens (not shown inFIG. 1) up to reactor A.

A radial-bed reactor is advantageously selected as reactor A in order tominimize the pressure drop through the catalytic bed. One or morereactors can be used. It is possible to use a reactor with one or morefixed beds or a reactor with one or more moving beds, coupled with acontinuous regeneration system. Two radial fixed bed reactors arepreferably used with a set of valves allowing permutation between a testphase and a regeneration phase.

It can be noted that, the reaction being globally exothermic, a heatexchange system known to the man skilled in the art allows to minimizethe energy consumption under normal running conditions.

Regeneration of the catalyst is generally carried out in an air stream.It is possible to recirculate the combustion air with or without waterin order to dilute the oxygen and to control the regeneration exothermy.In this case, the oxygen content at the reactor inlet has to be adjustedby means of makeup air. Regeneration is performed at a pressure rangingbetween the atmospheric pressure (0 MPa relative pressure) and thereaction pressure. The regeneration temperature is selected between 400°C. and 600° C.; it can vary during the regeneration process.Regeneration end is detected when there is no more oxygen consumption.

At the outlet of reactor A, reaction effluent (2) is kept at itsreaction pressure, except for the pressure drops in the equipments itflows through. The effluent is cooled below the dew point of water.Condensation of an organic liquid is thus simultaneously caused. It isfed into a device B allowing three-phase separation of a gas phase (3)notably consisting of ethylene, an organic liquid (4) (gasoline and gasoil) and an aqueous liquid (5) (water, unreacted ethanol, solubilizedhydrocarbons). Typically, this separator B can be a separating drumcontaining internals of baffle or mist separator type allowing tominimize the volume required for the organic liquid-aqueous liquiddecantation, on the one hand, and the organic liquid-organic gasdecantation on the other. The residence time in this internal isadvantageously greater than 1 minute in order to allow these phaseseparations to take place. The temperature of the separator is generallyselected so as to recover at least 80% of the gas oil fraction producedin the reaction. It can range for example from 60° C. to 200° C., for apressure of about 3 MPa.

Aqueous phase (5) at the separator outlet predominantly consists ofwater and solubilized hydrocarbons. Prior to being discharged, for fieldirrigation purposes for example, this aqueous phase is treated, theseparated oil being recovered for example in the trucks used forconveying the ethanol to the conversion site.

Organic liquid (4) contains less than 20% by weight of aromaticcompounds.

Implementation with Recycling

The man skilled in the art commonly defines the diesel pool as a groupof hydrocarbons whose boiling point can range between 150° C. and 370°C. It is well known to the man skilled in the art that gas oil isessentially characterized, in addition to its volatility, by its cetanenumber. It is also well known that the cetane number is favoured bylinear hydrocarbons having a low branching ratio, disadvantaged byaromatics and greatly branched chains, and finally greatly disadvantagedby hydrocarbons containing several aromatic rings, possibly adjacent(such as naphthalene).

These definitions being thus reminded, their effect as regards theinvention is that one attempts to carry out a conversion by successiveoligomerization of ethylene and/or addition of an ethylene to ahydrocarbon present in the reactor. This oligomerization mode has theadvantage of creating predominantly linear products, thus with an apriori good cetane number, if the desired distillation range of 150°C.-370° C. is reached. Unfortunately, product degradation reactions alsooccur. These reactions are essentially hydrogen transfer reactions thatdegrade the olefinic chains formed to naphthenic, then aromatic cycles.There are also reactions of isomerization of the linear hydrocarbonskeleton to iso-olefins and cracking reactions that limit the growth ofthe hydrocarbon chains.

This is the reason why, in a variant of the method according to theinvention diagrammatically shown in FIG. 2, one considers recycling theseparated gas phase to the inlet of the ethanoldehydration-oligomerization reaction, the object of recycling being topractically achieve the growth of the olefinic hydrocarbons that havenot yet reached the desired volatility.

The catalyst is then contacted with fresh ethanol to which a recycle ofunwanted products from the process has been added, the goal of recyclingbeing to end the conversion, essentially as regards the volatility ofthe products formed. Thus, the recycled gasoline from the process isagain oligomerized in the reactor, or ethanol from the dehydration ofthe fresh ethanol is added thereto. The overall boiling point of theproduct formed is thus significantly increased. Several successiverecycling procedures can be performed so as to weight up this gasolinesufficiently to make it compatible with the diesel pool in terms ofboiling point.

In this variant, the temperature of the separator can be adjusted so asto recycle a maximum amount of products unconverted to diesel up to thelight gasoline fraction.

The recycle rate is imposed by the temperature. Once the temperatureset, part of the products can be revaporized and the other part isdischarged.

Recycling can be carried out after simple evaporation of the lightfraction of the product. This evaporation can be achieved in a vesselproviding a product residence time above 1 minute, the vapour phasebeing thus separated from the organic liquid phase and from the aqueousliquid phase.

In order not to accumulate the inerts that are created in the process byhydrogen transfer to ethylene, thus forming ethane, part of the gases,generally 1 to 30% by mass, in most cases at most 10% by mass, isdischarged. This purge (3) predominantly contains ethylene, as well asCO, CO₂, CH₄ and hydrogen, and water traces. It can be advantageouslyused as fuel in the ovens of the process.

The rest, generally 70 to 99% by mass, in most cases at least 90% bymass, is recycled to the reactor inlet (stream 20). This fraction of thegas phase is generally subjected to recompression prior to beingre-injected to stage (a) in admixture with the fresh ethanol.

Part of the ethanol is also dehydrogenated to acetaldehyde, a productthat is unstable under the reaction conditions. This product then breaksup into CO, CO₂, CH₄ and H₂.

Implementation With Hydrogenation

In another advantageous variant of the method according to theinvention, as regards the liquid products obtained, organic liquid cut(4) obtained by the process, with or without recycling, can be led to ahydrogenation of the remaining olefins in order to achieve a cetanegain. This variant is diagrammatically shown in FIG. 3.

All or part of liquid effluent (4) is contacted, in a reaction zone C,with a hydrogen-rich gas over a catalyst containing for example a metalfrom group VIII, which can be palladium or nickel, on a support ofalumina or silica or silica-alumina type, in order to achievehydrogenation of the diolefins and/or hydro-isomerization and/orhydrogenation of the olefins.

The metal content generally ranges from 0.1 to 10% by mass in the caseof palladium and from 1 to 60% by mass in the case of nickel. Theoperating conditions of this hydrogenation in the liquid phase generallyinvolve LHSVs (liquid hourly space velocities) from 1 to 8 h⁻¹, atemperature between 100° C. and 250° C. at the reactor inlet and anoperating pressure between 2 and 5 MPa. The hydrogenation performance isvalidated by measuring the bromine number that is advantageously at most1 g Br/100 g, if it is desired to saturate all of the unsaturatedcompounds present in the cut.

Effluent (30) from reaction zone C predominantly contains hydrocarbonsthat, because of their boiling point range, can be incorporated in thediesel pool. It can be used directly in the commercial diesel orfractionated into a heavy gasoline cut and/or a kerosine cut and/or agas oil cut prior to blending in the diesel pool.

The following examples illustrate the invention. They are in no waylimitative. Example 1 is given by way of comparison.

The ethanol feedstock treated in these examples is an industrial ethanolwith an alcohol strength of 93%.

EXAMPLE 1 (Comparison)

A pilot plant with a traversed bed is fed with a mixture of 50% by massof alumina and 50% by mass of zeolite Y, in form of extrudates (thecatalyst is designated by USY and it is considered to be microporous).75 g catalyst are used.

Prior to the test proper, the solid is activated at 550° C. in an airstream for 2 h. This activation consists of a calcination aimed atcombustion of the oil and grease traces, and at drying of the catalystbefore using it.

75 g/h ethanol are injected onto this catalyst, with a nitrogen dilution(inlet and outlet nitrogen taken away from the balance calculation) of40 Nl/h. At the reactor outlet, the gas phase, the organic liquid phaseand the aqueous liquid phase are separated. The test lasts for 50 h. Norecycling is performed. The reaction conditions used are as follows:temperature 400° C., the reactor being isothermal and pressure 3 MPa.

Various balances are performed during the test. The mass balancespresented have been corrected of the water present with the feedstock(water removed from the feedstocks and the products). These balances arecarried out over a period of 8 to 12 h and end at the time indicated inthe line “feeding time”.

The material balance is given in table 2 below. TABLE 2 Bal- Bal- Bal-Bal- USY test (3 MPa) ance 1 ance 2 ance 3 ance 4 Feeding time (hours) 816 24 32 Feedstock EtOH Mass 100 100 100 100 Water ethanol removedfeedstock - product Aqueous phase Total aqueous yield 43.8 45.4 50.746.8 Organic phase Total organic yield 0 2.8 0 4.3 Gas phase Gashydrocarbon 56.7 49.9 45.5 46.5 H2 0.3 0.4 0.4 0.4 CO 0.6 0.8 0.8 0.8CO2 0.3 0.2 0.1 0.1 Total Gas Phase 57.9 51.3 46.8 47.8 Total 101.7 99.597.5 98.9

The experimental mass balance shows that the hydrocarbon liquid phaseproduced comes in small amounts, even though dehydration of the ethanolis complete.

The hydrocarbon part of the gas phase predominantly contains ethyleneand ethane, as well as C1, C3, C4 and C5 hydrocarbon traces, and smallamounts of CO, CO₂ and hydrogen.

The organic liquid formed contains hydrocarbons whose boiling pointranges between 20° C. and 400° C. The gas oil fraction contained in thisproduct is 50% by mass.

EXAMPLE 2 (According to the Invention)

A pilot plant with a traversed bed is fed with a commercial solid calledIS463, marketed by the Axens company (formerly Procatalyse), alsoreferred to as GOD200 (in-house designation). 75 g of gamma alumina typecatalyst with an external surface of 200 m²/g and pore volume of 0.59cm³/g are used. This catalyst is an acid catalyst, predominantlymesoporous.

Prior to the test proper, the solid is activated at 550° C. in an airstream for 2 h. This activation consists of a calcination aimed atcombustion of the oil and grease traces, and at drying of the catalystbefore using it.

75 g/h ethanol are injected onto this catalyst, with a nitrogen dilution(inlet and outlet nitrogen taken away from the balance calculation) of40 Nl/h. At the reactor outlet, the gas phase, the organic liquid phaseand the aqueous liquid phase are separated. No recycling is performed.The reaction conditions used are as follows: temperature 400° C., thereactor being isothermal, and pressure 3 MPa.

The duration of the test, 96 h 30, allowed to carry out 12 balances.Analyses on the aqueous and organic yields were carried out on balances2, 5, 7, 9 and 12.

Table 3 hereafter gives the material balance obtained in this example.TABLE 3 GOD200 test Bal- Bal- Balance (400° C.-3 MPa) ance 2 ance 5Balance 7 Balance 9 12 EtOH 100 100 100 100 100 Aqueous phase Water 33.635.0 36.4 35.1 33.8 HC aqueous yield 1.8 2.4 3.6 5.5 10.3 Total aqueousyield 35.4 37.4 40.0 40.6 44.1 Organic yield 18.4 17.0 11.8 8.1 5.2 Gasphase HC gas 38.6 40.7 46.9 48.9 48.9 H2 0.9 0.8 0.6 0.5 0.4 CO 2.0 2.01.2 0.9 0.6 CO2 0.9 0.9 0.7 0.5 0.3 Total gas phase 42.4 44.4 49.4 50.850.2 Total 96.2 98.8 101.2 99.5 99.5

The aqueous and organic phase analyses show the nature of the compoundsformed.

The amounts of liquid organic phase produced are clearly larger thanthose obtained with a microporous USY type catalyst.

In the organic yield, the olefinic compounds are the majority (onaverage about 50% by mass) and the C6 olefins are the majority of theolefins. There are also C4 and some C8. Surprisingly, 40% of thehydrocarbon fraction has a boiling point temperature above 150° C.,therefore compatible with the diesel pool. This fraction is constantthroughout the test. The organic liquid phase also contains about 15%aromatics.

The hydrocarbon part of the gas phase predominantly contains ethyleneand ethane, as well as C1, C3, C4 and C5 hydrocarbon traces, and smallamounts of CO, CO₂ and hydrogen.

A possibility to follow the quality of the products obtained by theprocess described in the example here above, is to obtain the simulateddistillation curve of these products. The simulated distillation is awell-known method by one skilled in the art, that is close to the ASTMdistillation such as described in “Raffinage et génie chimique, P.Wuithier, Edition Technip (1965), Tome I, p 7” and in the articles “Oil& Gas Science and Technology—Rev. IFP, Vol. 62 (2007), No. 1, pp. 33-42,Oil & Gas Science and Technology—Rev. IFP, Vol. 54 (1999), No. 4, pp.431-438.”

The simulated distillation curve given in FIG. 4 indicates thedistribution of the formed products in term of boiling temperature andrate. This graph shows that products into the distillation gap ofgasoline and diesel fuel are obtained by this process. The differentcurves represent the simulated distillation of the organic yieldscorresponding to the different balances of the Table 3. Thus, forexample in the case of the balances 7 and 9, 40% of the hydrocarbonfraction has a boiling point temperature above 150° C.

EXAMPLE 3 (According to the Invention)

A simulation of the method involving a stage of recycling the separatedgas phase was carried out.

As in the previous example, the catalyst used is the commercial solidIS463 (also bearing the in-house designation GOD200).

The ethanol feedstock is first flashed at 20° C. under 3 MPa, thenheated to 400° C. The ethanol is dehydrated to ethylene up to a reactionprogress rate of 97% and the oligomerization reaction is carried outwith an ethylene conversion progress rate of 40% per pass.

The recycled C4+compounds are oligomerized or the ethylene present isadded thereto, with a product distribution comparable to the reactionwithout recycling. After decrease of the temperature after the reactiondown to a value ranging between 50° C. and 200° C., the reaction mixtureis separated into three phases (aqueous, hydrocarbons and gas) at 3 MPa.

Table 4 hereafter gives the evolution of the gasoline and gas oil yieldsas a function of the temperature of the separator, considering a verylow purge, set to 0.1% by mass of the recycle loop. TABLE 4 T separator(° C.) 100 110 120 130 140 150 160 170 180 190 200 210 220 Recycle 2.02.1 2.3 2.4 2.6 2.8 3.0 3.4 3.9 4.7 6.1 8.9 17.5 Gasoline yield (%) 2828 28 28 28 28 27 27 26 24 21 17 10 Gas oil yield (%) 23 23 24 25 26 2728 29 31 34 37 42 49 Liquid yield (%) 50 51 52 53 54 55 55 56 57 58 5859 59

These values show that the amount of gas oil obtained increasessignificantly with the recycle ratio.

Simply to have an order of magnitude concerning the production of gasoil, assuming that it is possible to work with an available amount ofethanol of the order of 200,000 tons/year, under such conditions, at atemperature of 200° C. (recycle equal to 6), a gas oil yield of theorder of 74,000 tons/year and a gasoline yield of the order of 42,500tons/year would be reached, the rest being a production of water.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forthuncorrected in degrees Celsius and, all parts and percentages are byweight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications,cited herein and of corresponding French application No. 06/04.928,filed May 30, 2006, is incorporated by reference herein.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A method of converting ethanol to a base stock for diesel fuel,characterized in that it comprises: a reaction stage (a) of contactingthe ethanol with an acid catalyst, amorphous or structured,predominantly mesoporous, comprising at least 60% pores whose sizeranges between 2 and 50 nm, producing a gas phase, an organic liquidphase and an aqueous liquid phase, and a stage (b) of separating saidgas phase, said organic liquid phase and said aqueous liquid phase.
 2. Amethod as claimed in claim 1, wherein the acid catalyst, amorphous orstructured, predominantly mesoporous, of stage (a) comprises any ofdelta, gamma and eta aluminas or silica-aluminas.
 3. A method as claimedin claim 2, wherein said catalyst is a gamma or delta alumina ofexternal surface area ranging between 130 and 350 m²/g and of porevolume, measured by mercury intrusion, ranging between 0.3 and 1.2cm³/g.
 4. A method as claimed in claim 2, wherein said catalyst is anamorphous silica-alumina with a silica ratio ranging between 10 and 90%by mass and an external surface area ranging between 200 and 480 m²/g(SBET measurement).
 5. A method as claimed in claim 4, wherein saidsilica-alumina has a pore volume, measured by mercury intrusion, rangingbetween 0.5 and 1.5 cm³/g.
 6. A method as claimed in claim 1, whereinstage (a) is carried out at a temperature ranging between 300° C. and500° C., at a pressure ranging between 2 and 10 MPa and at a WHSV of 0.2to 4 h⁻¹.
 7. A method as claimed in claim 6, comprising a catalystregeneration stage.
 8. A method as claimed in claim 7, whereinregeneration is performed in an air stream at a pressure ranging betweenthe atmospheric pressure and the reaction pressure, and at a temperatureselected between 400° C. and 600° C.
 9. A method as claimed in claim 6,wherein stage (b) of separating said gas phase, said organic liquidphase and said aqueous liquid phase is carried out at the reactionpressure lowered by equipment pressure drops.
 10. A method as claimed inclaim 1, wherein at least part of the gas phase separated in stage (b)is recycled to an inlet of stage (a).
 11. A method as claimed in claim1, further comprising subjecting at least part of the organic liquideffluent from separation stage (b) to hydrogenation.
 12. A method asclaimed in claim 11, wherein hydrogenation is carried out by contactwith a hydrogen-rich gas over a hydrogenation catalyst containing ametal from group VIII, an alumina, silica or silica-alumina typesupport, at a LHSV of 1 to 8 h⁻¹, at a temperature ranging between 100°C. and 250° C. at the reactor inlet and at an operating pressure rangingbetween 2 and 5 MPa.
 13. A method as claimed in claim 12, wherein saidhydrogenation catalyst comprises 0.1 to 10% by mass of palladium.
 14. Amethod as claimed in claim 12, wherein said hydrogenation catalystcomprises 1 to 60% by mass of nickel.